Electric controllers frequently sample sinusoidal or sinusoidally excited signals to determine characteristics of the sinusoidal signals, and use the determined characteristics to control a component. Various types of signal sampling are possible, including phase-locked loops, Costas loops, and similar carrier phase recover methods. Typical sampling methods rely on fixed, uniform, periods between sample points.
Often it is useful to limit sampling in a digital system to certain significant phase angles of the input signal, for example to maximize signal-to-noise ratio of data points. Known methods of limiting sampling to specific phase angle values require the controller to generate the excitation signal, or require a relatively short sampling period compared to the reference signal period. Granting the excitation signal is not always feasible, and short sampling periods require additional processing time and memory utilization, particularly when the difference between desired sampling phases is non-uniform or certain phase angles are to be rejected.